1. Field of the Invention
This invention relates to a boomerang for sport, more particularly to a boomerang made from a flat sheet material of a reduced weight so as to ensure safety.
2. Description of the Related Art
Boomerangs, which have been used for sport in recent years, are devices capable of being thrown by a user, flying in a continuous path, and returning to the point of launching. Referring to FIGS. 1 to 3, two conventional boomerangs 5, 6 are shown to include two arms 51,52 and three arms 61, respectively. Each arm 51,52,61 is designed to have an airfoil thickness such that, when the boomerang 5,6 is thrown, air flows over its leading edge 511,521,611 and its trailing edge 512,522,612 to produce a lift force according to Bernoulli""s law, and the boomerang 5,6 continues rotation until it returns to the point of launching. As such, the boomerang 5, 6 is required to have a sufficient thickness in order to produce the desired lift, thereby resulting in a greater weight thereof, which in turn results in a larger flight range. Therefore, the conventional boomerangs 5, 6 generally cannot be used in a relatively narrow area.
To overcome the above problem, referring to FIGS. 4 and 5, another conventional boomerang 7 was proposed. The boomerang 7 is made from a thin plate, and is shown to include four arms 71, each of which has two bent portions 711,712 so as to reduce the overall weight of the boomerang 7. However, as the flight path of the boomerang 7 is monotonous, the boomerang 7 is not interesting to play with.
The object of the present invention is to provide a sport boomerang which is capable of adjustable flight patterns and which has an adjustable flight range.
According to this invention, the boomerang is made from a flat sheet material, and includes a central body with an outer periphery surrounding a center point. The central body has top and bottom surfaces that are substantially parallel to each other and that are symmetrical relative to a horizontal plane. A plurality of interconnecting portions are integrally formed with the outer periphery of the central body, and are angularly displaced from one another about the center point. Each of the interconnecting portions extends outwardly and along a radial axis, and terminates at a boundary region. A plurality of blades are integrally and respectively formed with the interconnecting portions, and are angularly displaced from one another. Each of the blades includes leading and trailing edges which are opposed to each other in one of clockwise and counterclockwise directions when the blades are turned about an axis that is normal to the horizontal plane and that passes through the center point, and which are symmetrical relative to a middle line. Each of the blades further includes a distal end which is opposed to the boundary region along the middle line and which joins the leading and trailing edges, respectively, at leading and trailing junctures. The middle line intersects the radial axis to form an obtuse included angle therewith, which faces towards the leading edge. Each blade further includes a bent line which extends towards the distal end and which is positioned between the middle line and the trailing edge. A bent portion, which faces towards the leading edge, is defined by the bent line and the trailing edge. The bent portion forms an obtuse included angle with the horizontal plane.